This invention relates to a clip-on ammeter in general and more particularly to a clip-on ammeter which permits obtaining improved measurement accuracy.
In conventional current measurements, it is necessary to sever the current carrying line and to insert into the line a measuring element, be it an ammeter or a measuring resistor, at which the voltage can be measured. Interrupting the line carrying the current to be measured can be avoided if a so-called clip-on ammeter is placed around the line. For a-c current, clip-on transformers have been in use for a long time. After technically usable Hall elements were introduced, clip-on ammeters also became possible for d-c current measurements.
As is well known, what is known as a Hall generator consists of a rectangular semiconductor chip, at the narrow sides of which contacts for feeding in a control current are attached. If this element is brought into the air gap of a magnetic frame or, more generally, into a magnetic field, then what is known as a Hall voltage can be taken off at appropriate contacts on its long sides.
The Hall voltage is proportional to the current through the Hall element and proportional to the magnetic flux going through the Hall element perpendicularly.
The conversion factor which appears in this relation between the Hall voltage, the magnetic flux and the control current, however, is not constant. It is subject to fluctuations which are due to the properties of the semiconductor material of the Hall element and also to the properties of the magnetic frame.